Motor control system



1941. J. L. HARRIS MOTOR CONTROL SYSTEM Filed March 29, 1940 2 Sheets-Sheet 1 John I4. Harris KB AW 79 W no 1 m 3 7 J 2 1 r 5 6 A u 6 S 3 we n I. H 5 1 In MI H o O 6 a... u. 8 l 9 u MW u 7: Mm m 5. HI I V 7 6 l8 u /5 ul 2 O u. 321 a l 3 O H o 3 e I l I. 1 9 6 6 ss f Oct. 14, 1941.

Filed March 29, 1940 2 Sheets-Sheet 2 l8% lee 8 Bl I HI H2 H3 may :ZIZ7

Q I fimnntor John L. Harris Patented Oct. 14, 1941 MOTOR CONTROL SYSTEM John L. Harris, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware 14'Claims.

The present invention relates to a motor control system and more particularly to one employing a relatively sensitive relay.

In numerous motor control systems, particularly of the type wherein the motor is controlled from a remote point, it is customary to employ a relatively sensitive relay. Particularly in the case where the energization of this relay is gradually varied to vary the position thereof, difliculty arises that when the control contacts are first engaged the contact pressure is inadequate to carry the motor current. It is accordingly quite common to employ booster means in connection with such relays. Where the relay is an electrically operated relay, such booster means may take the form of additional booster coils or means for additionally varying the current through the main relay coils upon the relay contacts being engaged. The use of such a booster means has the disadvantage, particularly in remote control systems of the proportioning type, that the sensitivity of the system is materially decreased. It will be obvious that after a booster force is applied, a considerable change in the energization of the relay is necessary before the relay will change its circuit controlling position.

An object of the present invention is to pro vide a motor controlling system employing a relay wherein upon the relay moving to motor operating position it is more firmly urged into such position by booster means and in which provision is made for periodically decreasing such booster action. In one embodiment of the invention, this is accomplished by removing or decreasing the booster force. In another modification this is accomplished by applying a further force opposing the booster force.

A further object of the present invention is to provide such an arrangement wherein the booster force is only momentarily removed,

A further object of the present invention is to provide such an arrangement in which it is impossible for the'motor to stop in any position wherein the booster force is not applied to the relay upon the initiation of a new operating cycle.

A further object of the present invention isto provide such an arrangement wherein application of the booster force is accomplished by changing the energization of the relay and wherein a snap'swltch operated by the motor is efiective to. periodically decrease this booster force.

Application March 29, 1940, Serial No. 326,688

A further objectof the present invention is to provide a motor control system wherein the booster action is decreased upon the motor operation being initiated and wherein the motor is periodically operated independently of the relay.

Other objects of the invention will be apparent from a consideration of the accompanying specification, claims and drawings, of which Figure 1 is a schematic view of one species of the improved motor control system;

Figure 2 is a schematic view of a portion of a modified system; and

Figure 3 is a schematic view of a portion of another modification of the system.

Referring to the drawings for a more detailed understanding of the invention, the invention is shown in Figure 1 In connection with the control of a motor In. This motor is illustrated as being of the reversible induction type having two rotors II and I2. Associated with the rotors- II and I 2 are field windings l3 and i4, respectively. It is to be understood that when field winding I3 is energized the motor is operated in one direction, and when field winding I4 is energized the motor is operated in the other direction. The rotors H and I2 are secured to a shaft I6 which is connected through a reduction gear train I! to a shaft 18. reduction gear train I! is an intermediate gear l9 secured to a shaft 20. The shaft I 8 has secured thereto a crank disc 2| which is connected through a link 22 to the valve stem 23 of a valve 24. Upon counter-clockwise rotation of shaft l8 and crank disc 2|, the valve stem 23 is moved upwardly to move the valve 24 to open position. Similarly, upon the opposite rotation of shaft l8, the valve 24 will be moved to closed position. Where the motor system is employed in connection with a temperature regulating system, the valve 24 may well regulate the flow of a temperature changing fluid such as steam through a pipe leading to radiators or other similar devices.

A relay 2'! controls the energization of motor I0. This relay is of the balanced type comprising a U-shaped armature member 28 pivotally mounted at 29. The armature member has two downwardly extending legs which cooperate with coils 3| and 32. Associated with the relays 2| and 22 are booster coils 33 and 34. Secured to the armature 28 is a switch blade 36 which is adapted to selectively engage fixed contacts 31 and 38. The switch blade 36 is secured to armature 28 by an insulated connection 40 of any suitable form. The position of armature 28 and switch blade 36 is determined by the relative en- Included in the ondary 58. Thus relay ergizations of relay coils 3| and 32, the action of these relay coils being affected by booster coils 33 and 34. Disregarding the booster coils, the relay switch blade 36 is in the position shown when relay coils 3| and 32 are equally energized. Upon relay coil 3| becoming more highly energized than relay coil 32, switch blade 36 is moved control potentiometer and comprises a resistance element 45 over which moves a contact arm 46. The contact arm 46 is secured to a bimetallic element 41 which variably positions the arm 46 in accordance with the temperature to which bimetallic element 41 is subjected. As indicated by legends C and H on the drawing, the bimetallic element is efiective to move contact arm 46 to the left upon a temperature fall and to the right upon a temperature rise. It is to be understood that the particular means for actuating contact arm 46 is of no particular importance so far as the present invention is concerned. The invention, however, is particularly applicable to a device such as a thermostatically operated potentiometer where the controlling force is necessarily relatively small.

The potentiometer 44 constitutes a rebalancing or follow-up potentiometer. This potentiometer comprises a resistance element 49 over which moves a contact arm 56. Contact arm 56 is pivotally mounted at and has secured thereto a yoke 52. Disposed between the two arms of the yoke 52 is a cam 53 driven by the shaft l8. It will be obvious that upon rotation of the shaft l8 in a clockwise direction, the contact arm 56 is moved to the left and upon a rotation of the shaft l8 in a counter-clockwise direction, the ,contact arm 56 is moved to the right. It will thus be observed that upon the position of valve 24 being varied, the position of contact arm 56 is similarly varied.

Power for operation of the system is supplied by a step-down transformer 56. This transformer comprises a line voltage primary 51 and a low voltage secondary 58. The primary winding 51 is connected to a suitable source of power (not shown).

The potentiometers 43 and 44 are connected in parallel with the relay coils 3| and 32 to the seccoils 3| and 32 are connected in series across the secondary winding 58 as follows: from the left-hand terminal of secondary 58 through conductors 66, 6| and 62, relay coil 3|, conductors 63 and 64, relay coil 32, and conductors 65, 66 and 61 to the other terminal of secondary 58. The resistance element 48 of potentiometer 44 is connected across relay coil 58 as follows: from the left-hand terminal of secondary 58 through conductors 66, 6| and 68, protective resistor 63, conductor 16, resistance element 49, conductor 1|, protective resistor 12, and conductors 13, 66 and 61 to the other terminal of secondary 58. The resistance element 45 of control potentiometer 43 is connected across the secondary 58 asfollows: from the left-hand terminal of secondary 58 through conductors 66, 6| and 68, protective resistor 69, conductors 16 and 14, resistance element 45, conductors and 1|, protective resistance element 12, and conductors 13, 66 and 61 to the other terminal of secondary 58. The contact arms 46 and 56 are both connected to the junction of relay coils 3| and 32. Contact arm 43 is connected as follows: bimetallic element 41, conductors 11 and 18 to the junction of conductors 63 and 64. Contact arm 56 is connected by the conductor 18 to the same junction.

It will be observed from the connections traced in the above paragraphs that the potentiometers 43 and 44 are connected in parallel with relay coils 3| and 32 and act as voltage dividers. Thus upon contact arm 43 being moved to the left as happens in connection with a temperature fall, the voltage across relay coil 32 is increased thereby unbalancing the energization of the relay and causing switch blade 36 to move into engagement with contact 31. Upon contact arm 46 moving 'to the right, the opposite action takes place. In other words, the energization of the relay coil 3| is increased and that of the relay coil 32 decreased. The rebalancing potentiometer 56 has a similar efiect upon the relative energization of relay coils 3| and 32. It will be apparent that for a given movement of contact arm 46 in one direction, the effect upon the energization of.

relay coils 3| and 32 can be overcome by an equivalent movement of contact arm 56 in the opposite direction. The apparatus is so designed that upon the energization of relay coils 3| and 32 being unbalanced by a movement of contact arm 46 in either direction, the motor is operated in such a direction as to move contact arm 56 in the opposite direction to rebalance the system.

In this manner, the motor is at all times operated to position the valve 24 in accordance with the position of contact arm 46. This operation will be more fully set out in connection with the description of the operation of the system as a whole.

In tracing the above connections, reference was made to the protective resistors 66 and 12. The purpose of these resistors is to prevent a condition wherein the secondary 58 would be completely short circuited. Inasmuch as a movement of contact arm 46 in one direction causes an operation of the motor such as to move contact arm 56 in the opposite direction, a condition can arise wherein the arms 46 and 56 are in extreme opposite positions. Thus when contact arm 56 is in its extreme left position and contact arm 46 in its extreme right position, if it were not for resistors 69 and 12, the secondary 58 would be short circuited as follows: from secondary 58 through conductors 66, 6|, 68, and 16,

. contact arm 56, conductor 11, bimetallic element 41, contact arm 46, and conductors 15, 1|, 13, 66, and 61 to the other terminal of secondary 58.

Limit switches 8| and 82 are provided to limit the movement of the motor. The limit switch 8| comprises a long resilient contact blade 83 and a relatively short rigid contact arm 84. Similarly, limit switch 82 comprises a long resilient contact blade 86 and a short rigid contact blade 85. An arm 88 of insulating material is secured to the shaft I8 and is adapted to engage the ends of the switch blades 83 and 86 upon rotation of the shaft I8 to positions corresponding to the desired extreme positions of movement of the valve. Thus when the shaft I8 is revolved in valve opening direction, the arm 88 will engage the switch blade 83 upon the valve approaching open position. Similarly, during closing movement of the valve, the arm 88 will engage the switch blade 86 at a predetermined minimum flow position. Upon arm 88 engaging either of switch blades83 or 86, the respective limit switches open to terminate energization of the motor.

A switch 90 controls the energization of the booster coils 33 and 34. two yieldable switch blades 9| and 92 which carry contacts 93 and 94, respectively. Switch blades 9| and 92 are secured in blocks 98 and 95. The blocks 98 and 95 have portions 96 and 91 projecting upwardly adjacent the inner faces of switch blades 9| and 92. The purpose of the upwardly projecting portions 96 and 91 is to limit the movement of switch blades 9| and 92 toward each other. In other words, by reason of these upwardly projecting portions 96 and 91, the switch blades 9| and 92 move more freely outwardly than inwardly. Secured to the outer surface of the upper end of switch blade 9| is a resilient blade 99. A similar resilient blade I is secured to the upper end of switch blade 92. A crank arm IOI is secured to shaft 20 and is adapted to cooperate with the resilient blades 99 and I00. It will be apparent that the resilient blades 99 and I00 readily flex outwardly inas-' much as they are secured to blades 9| and 92 at their lower ends. The resiliency of the blades 99 and I00 is much less than that of switch blades 9| and 92 sothat upon the crank arm IOI engagingthe inner surface of either of the blades 99 and I00, the associated switch blade is not moved. Upon the crank arm IIJI engaging the outer surface of the leaf springs however, the associated switch blade 9| is moved. Thus in the case in which the shaft 20 is revolved in a clockwise direction from the position shown, arm IOI flexes the blade 99 and does not disturb the position of contacts 93 and 94 until it has re-' volved through almost a complete cycle and engagesthe outer surface of the blade I00. A further counter-clockwise movement of the crank arm IOI results in switch blade 92 being moved to the left and inasmuch as contacts 93 and 94 are in abutting engagement, the motion of switch blade 92 will be transmitted to switch blade 9|. As soon as arm IOI has moved over the end of blade I00, the two switch blades 9'I and 92 will be free to travel back. The movement of switch blade 9| will be relatively limited, however, due to its engagement with the upstanding portion 96 of block 98. The movement of switch blade 92 on the other hand, will not be so restricted so that this switch blade 92 will swing considerably more to the right than will switch blade 9|. The result will be that contacts 93 and 94 will be momentarily separated. Upon the return movement of switch blade 92, contacts 93 and 94 will be reengaged. The action which thus results each time that contact arm IOI revolves through a complete cycle is that contacts 93 and 94 are momentarily separated. It is to be noted that as soon as a condition has been created whereby switch blades 93 and 94 will be separated, it is assured that these contacts will be reengaged. It is thus impossible for the motor to stop at any position wherein contacts 93 and 94 will remain separated. Upon contact arm I 0| revolving in the opposite direction, that is in a counterclockwise direction, the arm IOI will engage resilient blade 99 to move both switch blades 9| and 92 to the right. When the contact arm IOI clears the blade 99, the two switch blades will move back to the left. In this case, the movement of switch blade 92 is limited by the upstanding portion 91 while the movement of switch blade 9| is not so limited. Again, a momentary separation of contacts 93 and 94 will take place.

This switch comprises As in the case in which crank arm IIII rotates in a clockwise direction, it is impossible to create a condition wherein contacts 93 and 94 are left in a disengaged position.

Operation The various elements are shown in the drawing in the position occupied when the valve 24 is in an intermediate position. Thus in the illustrated application of the invention to the temperature control art, the positions are those occupied in which the temperature is at the desired value and the flow of heating fluid through valve 24 is substantially that required to maintain such a temperature. Let it now be assumed that the temperature does fall so as to cause contact arm 43 to be moved to the left. From the preceding description it will be obvious that this causes relay coil 32 to become more highly energized than relay coil 3|, thereby moving switch blade 36 into engagement with contact 31. Upon such engagement taking place, the following circuit is established to the field winding I3 of motor I0: from the left-hand terminal of secondary 58 through conductors 60 and I03, contact arm 36, contact 31, conductor I04, limit switch BI, conductor I05, field winding I 3, and conductors I06, I01 and 67 back to the secondary 58.

The motor is so designed that upon field winding I3 being energized, the motor is rotated in such a direction as to cause counter-clockwise movement of the shaft I8 and clockwise movement of the shaft 20. The counter-clockwise movement of the shaft I8 results in a similar movement of the crank disc 2| and resultant movement of the valve 24 towards open position. At the same time, the counter-clockwise rotation of the shaft I8 causes the contact arm 50 to be moved to the right which is in the direction opposite to the original movement of the contact arm 46 that caused the unbalance in the energization of the relay. It will be obvious that after the motion has continued sufficiently far, the movement of the contact arm 50 to the right will result in the relay being rebalanced.

Disregarding the effect of the relay coils-33 and 34, as soon as the relay coils 3| and 32 are again equally energized, the relay will move to the neutral position and terminate the energizationof the field winding I3. The motor will thus have moved the valve an amount proportional to the movement of contact arm 46. Where the system is employed in connection with temperature control, this will result in an increased flow of heating fluid in accordance with the decrease in temperature in the space in which the bimetallic element 41 is located.

The action which has just been described is that which would take place if the booster coils 33 and 34 were not present. Upon switch blade 36 engaging the contact 31 in the manner previously described, an energizing circuit is not only established to the field winding I3 but is also established to the booster coil 34 as follows: from the secondary 58 through conductors 60 and I03, blade 36, contact 37, conductor I04, limit switch 8|, conductors I05 and I09, booster winding 34, conductor I I0, block 98, switch blade 9|, contacts 93 and 94, switch blade 92, block 95, and conductors II3, I01 and 61 to the other terminal of secondary 58. The energization of the booster winding 34 as the result of the establishment of the above circuit instantly results in a force aiding that exerted by winding 32 so that the switch blade 36 is moved more firmly into engagement to the point where it exerts a force equal to that exerted by both coils 32 and 34. As soon as this condition is attained, the switch blade 36 is separated from the contact 31 thereby deenergizing the booster coil 34. This results in the relay coil 3| now being more highly energized than the relay coil 32 and tending to cause the switch blade 36 to move into engagement with the contact 38. It will be readily apparent that the provision of the booster coil 34 thus necessitates a wider operating differential for the relay. If the relay is not provided with a relatively wide operating differential, the motor will continue to operate in first one direction and then another due to the unbalance effect introduced by the booster coil. Where a relay is provided with a wide differential as is usually the case, the available number of positions is materially decreased.

As indicated in an earlier portion of the specification, the present invention is particularly concerned with periodically decreasing or removing the booster effect so that the relay is subjected only to the forces exerted by the regular control means. It will be recalled that upon the shaft l8 being revolved in a counter-clockwise direction, the shaft 29 is revolved in a clockwise direction. As previously described, this results in the switch blades 9| and 92 both being moved to the left and then being released to move back towards the right by reason of their inherent resiliency. The switch blade 92 will be free to move further than the switch blade 9| so that the contacts 93 and 94 will be momentarily separated. This momentary separation of i the contacts 93 and 94 will occur during each revolution of the shaft 29. Since shaft 29 is connected in an intermediate point of the gear train, this shaft will revolve at a relatively high rate of speed as compared with the shaft If! so that the contacts 93 and 94 will be separated at relatively frequent intervals. Each time that the contacts 93 and 94 are separated, the circuit previously traced through the booster coil 34 is interrupted. If the movement of the contact arm 59 at any one of these intervals at which contacts 93 and 94 are separated has been sufficient to rebalance the energization of the coils 3| and 32, the relay switch blade 36 will separate from the contact 31, thereby terminating further movement of the motor.

energization of the coils 3| and 32 and will not be continued until the force exerted by the relay coil 3| is equal to that exerted by both relay coils 32 and 34. The relay can thus be provided with a much narrower differential and much more sensitive operation of the system can be obtained.

The operation which has just been described is that which occurs when the contact arm 46 has moved to the left. Let it be assumed that the temperature rises so that the contact arm 46 is moved to the right. This will cause the relay coil 3| to become more highly energized than therelay coil 32 so that .the switch blade at is moved into engagement with the contact 38. .Upon this taking place, a circuit is established Thus the operation of themotor will be terminated upon a rebalance of 'by the mechanism driven by the motor.

to the motor field winding l4 as follows: from the left-hand terminal of the secondary 58 through conductors 69 and I93, switch arm 36, contact 38,

conductor H5, limit switch 62, conductors H6- and H1, field winding l4, and conductors I96, I91 and 61 to the other terminal of secondary 58. The energization of the field winding |4 will cause the motor l9 to revolve in the opposite direction so as to cause clockwise movement of the shaft l8 and crank disc 2|. This will cause movement of the valve 24 towards closed position and a movement of the contact arm 59 to the left. At the same time, the shaft 29 will be rotated in a counter-clockwise direction. Simultaneously with the energization of the field winding M, the booster winding 33 is energized by a circuit as follows: from the left-hand terminal of secondary 58 through conductors 69 and I93, switch blade 36, contact 38, conductor H5, limit switch 92, conductors -||6 and H9, booster coil 33, conductors I29 and H9, block 96, switch blade 9|, contacts 93 and 94, switch blade 92; block 95, and conductors 3, I91 and 61 to the other terminal of secondary 58. The energization. of the booster coil 33 results in a booster force aiding that of the winding 3| so as to move the switch blade 36 more firmly into engagement with the contact 38. A firm engagement of the switch blade 36 with the contact 36 is thus effected in order to eliminate any possibility of sparking between the switch blade and the contact 36.

As pointed out previously, the shaft 29 is now rotated in a counter-clockwise direction. Each time that the contact arm |9| engages the leaf spring 99, the switch blades 9| and 92 are moved to the right as previously described. Upon being released, the two switch blades move to the left but the movement of the switch blade 92 is restricted by the upstanding shoulder 91 whereas the movement of the switch blade 9| is not so restricted. The result is that the contacts 93 and 94 are momentarily separated. Such momentary separation of the contacts 93 and 94 occurs each time that the crank arm |9| makes a complete revolution. Each time that the contacts 93 and 94 are so separated, the booster coil 33 is deenergized so that the position of the switch blade 36 is determined entirely by the relative energization of the relay coils 3| and 32. Thus each time that these contacts 93 and 94 are separated, an opportunity is aiforded the relay to rebalance itself if the position of the contact arm 59 corresponds to the position of the contact arm 46.

A very important feature of the present invention is that the contacts 93 and 94 are separated This results in an extremely simple system while at the same time provision is made for securing adequate contact pressure between the cont-acts 93 and 94. As pointed out previously, it is a particularly important feature of. the invention that the contacts 93 and 94 are never separated more than momentarily and that it is impossible for the motor to be stopped at any position wherein the contacts 93 and 94 are maintained out of engagement.

' Species of Figure 2 In the species of Figure 1 the periodic decrease in booster action is accomplished by deenergization of the booster coil. In the species of Figure 2, this decrease in booster action is accomplished by. the energization of a separate booster coil which opp ses a first booster coil.

Inasmuch as certain elements of the system of Figure 2 are identical to those of Figure 1, only a portion of the complete system is shown in Figure 2, and certain elements shown in greater detail in Figure 1 are shown in schematic form in Figure 2. In order to more clearly bring out the analogy between the two systems, certain elements of Figure 2 which are identical to the system of Figure 1 have had similar reference characters applied thereto. Thus the relay I21 is shown as comprising an armature 28 and a switch blade 36 which cooperates with contacts 31 and 36. The armature has cooperating therewith two main relay coils 3I and 32, the relative energization of which is controlled-by rebalancing potentiometers as in Figure. l. The conductors 62, 68, 69, 65, and 13 are identical to the same conductors in Figure l and lead to the same elements. Associated with the relay coils 3| and 32 are booster coils I33 and I34. The action of the booster coils I33 and I34 is opposedby auxiliary coils I35 and I36. Thus the booster coil I33 aids the coil 3I and is opposed by coil I35. Similarly, the coil I34 when energized aids the coil 32 and is opposed by the coil I36 when the relay is energized. The auxiliary coils I35 and I36, may, if desired, be so formed as to exert a slightly greater force than their associated booster coils I33 and I34 so that when either auxiliary coil is energized, it not only neutralizes the effect of the booster coil but introduces a slight additional force tending to move the relay back to its balanced position. This is desirable since a relay of this type tends to have a slight amount of inertia.

7 and gear train I1 are shown within a box I40.

Projecting from this box are the shafts I8 and 20. The box I40 is provided with three terminals I4I, I42 and I43. The terminal I42 is the terminal common to field windings I3 and I4, while terminal I H is connected to the field winding I3 and the terminal I43 to field winding I4.

A switch I50 is provided for controlling the energization of the auxiliary windings I35 and I36. This switch comprises a pair of resilient switch blades II and I52 secured to an insulating block I53. The switch blades I5I and I52 carry contacts I54 and I55, these contacts normally being out of engagement. Secured to switch blades I5I and I52 are relatively thin resilient blades I56 and I51. The blades I56 and I51 are adjacent the blades I5I and I52 for the greater portion of the length of the blades I56 and I51. The blades I56 and I51 are secured to the inner sides of the blades I'5I and I52 so that they are free to flex inwardly but cannot readily flex outwardly. .A crank arm I59 is secured to the shaft and cooperates with the blades I56 and I51. Upon crank arm I59 engaging eitherblade I56 or I51 bymoving inwardly, the blade I56 or,I51, as the case may be, freely flexes. However, when the arm I59 engages the blade I 56 or I51'in moving outwardly, the corresponding switch blade I5I or I52 is moved therewith. Thus upon the crank arm I59 revolving in a clockwise direction, the crank arm I59 first engages the switch blade I51 which is freely flexed permitting the crank arm I59 to ride thereover without affecting the position of the switch blade I52. Upon further movement of the crank arm I59, it engages the inner surface of the upper end of the blade I56 causing the switch blade I59 to be moved outwardly to crank arm I59 passes over the upper end of the blade I56 permitting the switch blade I5I to return to the right by reason of its inherent resiliency. Upon returning to the right, contacts I54 and I55 will be momentarily moved into engagement and then separated. It will be noted that when the switch blades I5I and I52 are in such condition as to permit engagement of the contacts I54 and I55, it is impossible for these two contacts to remain in engagement.

A similar action will take place when the crank t e left. This movement will continue until the arm I59 is revolving in a counter-clockwise direction. In this case, the crank arm will flex the blade I56 so as not to affect the switch blade I5I. Thereafter, the switch blade I52 will be moved to the right until crank arm I59 passes over the end of the blade I51. The switch blade I52 is then able to spring back to the left carrying contact I55 into engagement with the contact I54. This engagement again is a momentary one, and it is impossible for the apparatus to assume any position wherein engagement of the contacts I 54 and I55 is continuously maintained.

Operation of species of Figure 2 As in the case of the species of Figure 1, the various elements of Figure 2 are shown in the position occupied when the relay is balanced and motor I40 is not being operated. Let it now be assumed that the temperature drops so as to cause the relay coil 32 to become more highly energized than the relay coil 3I as described in connection with Figure 1. This will cause switch blade 36 to be moved into engagement with contact 31 so that an energizing circuit will be established to motor I40 as follows: from the left-hand terminal of transformer 66 through conductor I64, switch blade 36, contact 31, conductor I65, limit switch 8|, conductors I66 and I61, motor terminal I, motor I40, motor terminal I42, conductors I68, I69 and I10 to the right-hand terminal of transformer 56. The establishment of this circuit, as in the case of Figure 1, will cause the motor to rotate in a direction to move the valve towards open position to move the shaft I8 in a counter-clockwise direction and the shaft 20 in a clockwise direction.

At the same time as the above traced circuit to motor I40 is established, a circuit is established to the booster coil I34 as follows: from the righthand terminal of transformer 56 through conductor I64, switah arm 36, contact 31, conductor I65, limit switch 6|, conductors I66, I12 and I13, booster coil I 34, and conductors I15 and I10 to the other terminal of transformer 56. The energization of the booster coil I34 produces a force aiding that exerted by the relay coil 32 so that the switch blade 36 is more firmly pressed into engagement with contact 31.

The revolution of the shaft 20 in a clockwise direction causes the arm I59 to periodically engage the resilient blade I 56. As previously described, upon the inner' surface of this blade being engaged by arm I59, the blade I5I is moved outwardly and allowed to spring back momentarily so as to effect engagement of the contacts I54 and I55. Such engagement of the contacts I54 and I55 thus occurs during each revolution of the arm I59. Each time that the contacts are so engaged, a circuit is established to the bucking coil I36 as follows: from the left-hand terminal of the transformer 56 through conductor I 64, switch blade 36, contact 31. conductor I65, limit switch 81, conductors I66 and I12,

bucking coil I36, conductor I11, switch blade II, contacts I54 and I55, switch blade I52, and conductors I16, I69 and I to the other terminal of the transformer 56. As previously explained, the bucking coil opposes the booster coil I34. Thus each time that contacts I54 and I55 are moved into engagement, the booster effect is counteracted. One advantage of the present arrangement is that it is possible to decrease the booster action any desired amount by properly proportioning the booster and bucking coils. As previously explained, the bucking coils may be designed so as to have a greater eifect than the booster coils. In this case, the energization of the booster coil I36 not only completely counteracts the effect of booster coil I34 but also introduces a slight force tending to rebalance the relay and thus overcome any inertia in the movable portions of the relay.

When the relay is unbalanced in the opposite direction as a result of the temperature rise, or in other words when relay coil 3| is more highly energized than the relay coil 32, the switch blade 36 is moved into engagement with the cont-act 38 and the following circuit is established to the motor I40: from the left-hand terminal of transformer 56, through conductor I64, switch blade 36, contact 38, conductor I19, limit switch 82, conductors I80 and I8I, motor terminal I43, motor I40, motor terminal I42, and conductors I68, I69 and I10 to the other terminal of the transformer 56. The establishment of this circuit causes the motor to rotate in a direction opposite to that previously discussed so that the shaft I8 is rotated in a clockwise direction and the shaft 20 in a counter-clockwise direction.

When the relay is unbalanced in the manner just described, an energizing circuit is established to the booster coil I33 as follows: from the left-hand terminal of transformer56 through conductor I64, switch blade 36, contact 38, conductor I19, limit switch 82, conductor-s I80, I83 and I 84, booster coil I33, conductors I85, I and I10 to the other terminal of transformer 56. The counter-clockwise rotation of the shaft causes the crank arm I59 to periodically engage the inner surface of the blade I51 so as to cause the contacts I54 and I55 to be momentarily snapped into engagement. Each time that such momentary engagement occurs, a circuit is established to the booster coil I35 as follows:

from the left-hand terminal of transformer 56 through conductor I64, switch blade 36, contact 38, conductor I19, limit switch 82, conductors I80 and I83, bucking coil I35, conductors I81 and I11, switch blade I5I, contacts I54 and I55, blade I52, and conductors I16, I69 and I10 to the other terminal of transformer 56. Each time that the bucking coil I35 is energized, the booster action of booster coil I33 is neutralized and a slight opposing force is introduced. Thus again, the boo-sterefiect is periodically eliminated and the relay is periodically subjected momentarily to a force tending to rebalance it.

It will be noted that the circuits to both the booster and bucking coils are controlled by switch blade 36 and its associated contacts. Thus, as soon as the relay is rebalanced, .the bucking and booster coils are both deenergized.

' coil is deenergized immediately after the motor is placed in operation. In order to guard against sparking and other disadvantages resulting from insecure engagement of the relay contacts, provision is made for periodically energizing the motor through a maintaining circuit independent of the relay contacts. As in the case of Figure 2, only a portion of the complete system is shown and the various elements which are identical to the elements of Figure 1 have the same reference numerals applied thereto. As in Figure 2, the entire motor assembly including the motor and gear train has been shown enclosed in a casing and is designated by the reference numeral I40. A switching mechanism designated by the numeral I84 is employed to periodically establish the maintaining circuit to the motor and to deenergize the booster coil. This switch assembly comprises two rigid switch blades I85 and I86 and a yieldable switch blade I81. These three blades are separated by insulating blocks I88 and I89. Switch blades I 85 and I86 carry contacts I 90 and I9I which are adapted to engage contacts I92 and I93, respectively, carried by the switch blade I81. The switch blade I81 has an extended portion I separated from the main portion by an insulated connection I96. The extended portion I95 is adapted to cooperate with two flexible switch blades I91 and I98. Switch blades I91 and I98 carry contacts I99 and 200 which are adapted to cooperate with contacts 20I and 203, respectively, carried by the extended portion I95 of the switch'blade I81. The extended portion I95 of the switch blade I81 is adapted to cooperate with a cam 205 secured to the shaft 20. The cam 205 has a notched portion 206. When the notched portion 206 is adjacent the extended portion I95, the switch blade I81 occupies the neutral position shown in the drawing. Upon rotation of the cam in either direction, the switch blade I81 is correspondingly moved so as to move one or the other of its contacts I92 and I93 into engagement with the associated contacts of the switch blades I85 and I86. At the same time, one or the other of the flexible blades I91 and I98 is moved so as to cause interruption of the circuit including con-' tacts I99, 20I, 203 and 200. Thus when the cam 205 rotates in a clockwise direction, the switch blade I81 is moved to the left. This causes engagement of the contacts I90 and I92. At the same time, the extended'portion I95 is moved sufflciently to the left to separate contacts 203 and 200. If on the other hand, the cam 205 is rotated in a counter-clockwise direction, contacts I 93 and I9I are moved into engagement and contacts I99 and 200 are separated.

Operation of species of Figure 3 assumed that the temperature changes so as to cause the relay coil 32 to be more highly energized than the relay coil 3I. Under these conditions, switch blade 38 will be moved into engagement with the contact 31' and the following circuit will be established to the motor I40: from the lefthand terminal of transformer 56 through conductors 208, 209 and 2| 0, switch blade 36, contact 31, conductors 2H and 2I2, limit switch 8|, conductors 2I3 and 2I4, motor terminal I II, motor I40, motor terminal I42, and conductors 2I5, 2I6 and 2I1. The establishment of this circuit causes the shaftI8 to revolve in a counterclockwise direction to move the valve towards open position, as previously described. At the.

same time, the shaft is revolved in a clockwise direction.

The engagement of the switch blade 36 with the contact 31 also established the following energizing circuit to the booster coil 34: from the left-hand terminal of transformer 56, through conductors 208, 209 and 2I0, switch blade 36, contact 31, conductors 2H and 2I2, limit switch 8|, conductors H3 and 2I9, booster coil 34, conductor 220, switch blade I91, contacts I99, 20I, 203 and 200, switch blade I98. and conductors 22I, 2I6 and 2". It will be noted that in the circuit to the booster coil 34 just traced, the contacts I99, 20I, 203 and 200 are included in series.

.As soon as the motor I is placed in operation, the cam 205 is revolved. In the case of the motor circuit traced in the above paragraph, the rotation of the shaft 20 is in a clockwise direction so that the cam 205 rotates in a clockwise direction. This clockwise rotation of the cam 205, as previously explained, causes the switch blade I81 to move the contact I92 into engagement with the contact I90. Just prior to this engagement being effected, the contact 203 is moved out of engagement with the contact 200. The separation of the contact 203 from the contact 200 results in the interruption of the previously traced circuit to the booster coil 34 so that the relay is now free to move to its neutral position as soon as the energization of the coils 3| and 32 is the same. When contact I92 moves into engagement with the contact I90, the following circuit to the motor I40 is established: from the left-hand terminal of transformer 56 through conductors 208 and 222, switch blade I61, contacts I92 and I90, switch blade I65, conductors 223 and 2I2, limit switch 8|, conductors 2| 3 and 2, terminal I, motor I40, terminal I42 and conductors 2I5, 2I6 and 2I1 to the other terminal of the transformer 56. It will be noted that this circuit is to the same terminals of the motor I40 as the circuit previously traced but is independent of the relay switch blade 36 and contact 31. The result is that the motor will continue to revolve until the notched portion 206 again is adjacent to the end of the extended portion I95 of the switch blade I81. If at this time the movement of the rebalancing potentiometer by the motor has caused a rebalance in the energization of' the relay coils -3I and 32, the motor will stop. If switch blade 36 is still in engagement with the contact 31, the cycle just traced will be repeated. The result is that the booster coil is periodically deenergized and the motor is run on a maintain-- ing circuit independent of the relay. The result is that the motor will normally be deenergized as a result of the separation of the contacts I90 and I92. Since these contacts are driven by the motor I40, they can be contacts of large current carrying capacity and have considerable pressure applied thereto. Because of this, the possibility of any harmful sparking between the contacts is minimized.

When the relay becomes unbalanced in the other direction as to cause switch blade 36 to engage the contact 38, a circuit will be established to the motor I40 as follows: from the left-hand terminal of transformer 56, through conductors 208, 209 and 2I0, switch blade 36, contact 38, conductors 225 and 226, limit switch 82, conductors 221 and 228, terminal I43, motor I40, terminal I42, and conductors 2I5, 2I6 and 2H. The establishment of this -circuit causes the motor to rotate in the opposite direction so that the valve is moved towards closed position, the

' 36, contact 38, conductors 225 and 226, limit switch 82, conductors 221 and 230, booster coil '33, conductors 23I and 220, switch blade I91,

contacts I99, MI, 203 and 200, switch blade I98 and conductors 22I, 2I6 and 2H to the other terminal of transformer 56. It will be noted that the circuit to the booster coil 33, like the circuit to the booster coil 34, is through contacts I99,

20I, 203 and 200 in series.

Upon the shaft 206 being revolved in a counterclockwise direction as a result of the operation of the motor, the extended portion I95 of the switch blade I81 is deflected to the right to cause separation of th contacts I99 and 2M. Immediately thereafter contacts I93 and I9I are moved into engagement. The separation of contacts I99 and NI causes the deenergization of the booster coil 33 so that the relay is free to rebalance when relay coils 3| and 32 are equally energized. The engagement of contacts I93 and I9I results in the following circuit being established to the motor I40: from the left-hand terminal of transformer 56 through conductors 208 and 222, switch blade I81, contacts I93 and I9I, switch blade I86, conductors 232 and 226, limit switch 82, conductors 221 and 228, terminal I43, motor I40, terminal I42, and conductors 2I5, 2I6 and 2I1 to the other terminal of transformer 56. This circuit, it will be noted, is independent of the relay so that the motor will continue in operation until the notched portion 206 is again adjacent the end of the extended portion I95 of the switch blade I81. If the relay is balanced at this time, the motor will stop. If not, the cycle will be repeated.

It will be noted that there is no possibility of the booster coil circuits being left in an open circuit position. This is due to thefact that the booster coil circuit is made immediately following the separation of the maintaining circuit contacts. While these contacts are remade while the motor may still be coasting slightly, the closing of these contacts will not unbalance the relay if the relay switch blade has moved to its neutral position in the meantime. This is due to the fact that the booster coil circuits are through the relay contacts.

The system of Figure 3 thus provides an arrangement whereby the starting of the motor is energized by a relay provided with ample booster action which is removed as soon as the motor is started. Furthermore, the stopping of the motor is under the control of relatively heavy contacts which are positioned by the motor itself.

The result is that the system is much more sensitive than prior art systems and at the same time it is assured that the various contacts are never subjected to loads which they are not properly designed to carry.

While I have shown several embodiments of my invention for purposes of illustration, it is to be understood that the invention is limited only by the scope of the appended claims.

I claim as my invention:

1. In a motor control system, a motor, an electrically operated relay controlling the operation of the motor, said relay having winding means and armature means, said armature means being movable into and out of a motor operating posidirection to cause said armature means to assume more firmly said motor operating position, and means operated by said motor upon continuous unidirectional movement thereof periodically to restore the effective energization of said winding means to more nearly the value determined by said control means.

2. In a motor control system, a motor, an electricallyoperated relay controlling the operation of the motor and movable into and out of a motor operating position in accordance with the energization of said relay, control means for varying the energization of said relay, means operative uponsaid relay being moved to said motor operating position to change the efiective energization of said relay in a direction to cause it to assume more firmly said motor operating position, and means operated by said motor periodically 'to energize said relay in a manner to oppose the change in the energization thereof introduced by said previously named means.

3. In a motor control system, a motor, an electrically operated relay controlling. the operation of the motor and movable into and out of a motor operating position in accordance with the energization of said relay, control means for varying the energization of said relay, means operative upon said relay being moved to said motor operating position to change the efiective energization of said relay in a direction to cause it to assume more firmly said motor operating position, and means including a snap switch operated by said motor effective upon continuous unidirectional movement of said motor to periodically restore the efiective energization ofsaid relay to more nearly the value determined by said control means.

4. In a motor control system, a motor, an electrically operated relay controlling the operation of the motor and movable into and out of a motor operating position in accordance/with the energization of said relay, control means for varying the energization of said relay, means operative upon said relay being moved to said.

motor operating position to change the efiective energization of said relay in a direction to cause it to assume more firmly said motor operating position, and means including a snap switch periodically moved by said motor from a first normal circuit controlling position to a second circuit controlling position, said switch when so moved immediately moving back to said first position independently of said motor, said last named means being operative each time that said snap switch moves to said second position to restore the effective energization of said relay to more nearly the value determined by said control means.

5. In a motor control system, an electrical motor, an electrically operated relay controlling theenergization of said motor, said relay comprising coil means and contacts the spacing of which is varied in accordance with the energization of said coil means, said coil means comprising a main portion and a booster portion, control means for varying the energization of the main portion of said coil means, means operative upon said relay contacts being moved into engagement to energize the booster portion of sai coil means in such a manner as to increase the contact pressure between said contacts, and means operated by said motor upon continuous unidirectional movement thereof alternately to energize and deenergize effectively the booster portion of said coil means, said last-named means operating so as to make the periods of efiective deenergization short as compared to the periods of energization.

6. In a motor control system, an electrical motor, an electrically operated relay controlling the energization of said motor, said relay comprising coil means and contacts the spacing of which is varied in accordance with the energization of said coil means, said coil means-comprising a main portion and a pair of mutually opposing booster portions, control means for varying the efiective energization of the main portion of said coil means, means operative upon said relay contacts being moved into engagement to energize one of said booster portions to increase the contact pressure between said contacts, and means operated by said motor periodically to energize the opposing booster portion of said relay.

-'7. In a motor. control system of the follow-up type, a reversible motor, an electrically operated relay controlling the operation of said motor and movable into and out of either of two motor operating positions in accordance with the energization of said relay, a variable control impedance controlling the energization of said relay, a variable follow-up impedance positioned by said motor and controlling the energization of said relay, means operative upon said relay being moved to either of said motor operating positions to change the effective energization of said relay in a direction tocause itto assume more firmly said motor operating position, and means operated by said motor after an initial movement thereof in either direction to restore the efiective energization of said relay to more nearly the value determined by said control and follow-up impedances.

8, In a motor control system of the follow-up type, a reversible motor, an electrically operated relay controlling the operation of said motor and. movable into and out of either of two motor operating positions in accordance with the energizationof said relay, a variable control impedance "controlling the energization of said relay, a variable follow-up impedance positioned by said motor and controlling the energization of said relay, means operative upon said relay being moved to either of said motor operating positions to change the effective energization of said relay in a direction to cause it to assume more firmly said motor operating position, and means operated by said motor upon continuous movement thereof in either direction periodically to restore the effective energization of saidrelay to more nearly the value determined by said control and follow-up impedances.

9. In a motor control system of the follow-up type, a reversible motor, an electrically operated relay controlling the operation of said motor and movable into and out of either of two motor operating positions in accordance with the energization of said relay, a variable control impedance controlling the energization of said relay, a variable follow-up impedance positioned by said motor and controlling the energization of said relay, means operative upon said relay being moved to either of said motor operating positions to change the efiective energization of said relay in a direction to cause it to assume more firmlysald of said relay, being moved to either of said motor operating motor operating position, and means operated by said motor upon continuous movement thereof in either direction periodically to energize said relay in a manner to oppose the change in the energization thereof introduced by said previously named means.

10. In a motor control system of the followup type, a reversible motor, an electrically operated relay controlling the operation of said motor and movable into and out of either of two motor operating positions in accordance with the energization of said relay, a variable control impedance controlling the energization of said rey. by said motor and controlling the energization of said relay, means operative upon said relay being moved to either of said motor operating positions to change the effective energization of said relay in a direction to cause it to assume more firmly said motor operating position, means operated by said motor after an initial movement thereof in either direction to restore the efiective energization of said relay to more nearly the value determined by said control and follow-up impedances, and means for periodically maintaining said motor in operation independently of said relay after said motor has been started.

11. In a motor control system of the follow- I up type, a reversible motor, an electrically operated relay controlling the operation of said motor and movable into and out of either of two motor operating positions in accordance with the energization of said relay, a variable control impedance controlling the energization of said relay, by said motor and controlling the energization means operative upon said relay positions to change the effective energization of said relay in a direction to cause it to assume more firmly said motor operating position, and switching means periodically operated by said motor through a predetermined cycle whenever said motor is operated in either direction, said switching means being operative during each cycle to first cause the eflective energization of said relay to be restored to more nearly the value determined by said control and follow-up impedance and to then cause said motor to be operated independently of said relay.

12. In a motor control system, a rotary electric motor, a device positioned thereby, a reduction gear train between said motor and said positioned device, an electrically operated relay controlling a variable follow-up impedance positioned.

a variable follow-up impedance positioned the energization of said motor, said relay having winding means and armature means, said armature means being movable into and out of a motor energizing position in accordance with the energization of said winding means, control means for varying the energization of said winding means, means operative upon said armature means being moved to said motor energizing position to change the effective energization of said winding means in a direction to cause said armature means to assume more firmly said motor energizing position, and means including a switch and actuating means therefor connected to said gear train at an intermediate point thereof, said last named means being effective upon initial rotation of said motor to restore the effective energization of said winding means to more nearly the value determined by said control means.

13. In a motor control system, a rotary electric motor, a device positioned thereby, a reduction gear train between said motor and said positioned device, an electrically operated relay controlling the energization of said motor and movable into and out of a motor energizing position in accordance with the energization of said relay, control means for varying the energization of said relay, means operative upon said relay being moved to said motor energizing position to change the effective energization of said relay in a direction to cause it to assume more firmly said motor energizing position, and means including a switch and actuating means therefor connected to said gear train at an intermediate point thereof, said last named means being effective periodically to restore the effective energization of said relay to more nearly the value determined by said control means and to operate the motor independently of said relay.

14. In a motor control system, a motor, an electrically operated relay controlling the operation of the motor and movable into and out of r a motor operating position in accordance with the energization of said relay, control means for varying the energization of said relay, means operative upon said relay being moved to said motor operating position to change the effective energization of said relay in a direction to cause it to assume more firmly said motor operating position, and means operating concurrently with said motor for periodically causing a change in the energization of said relay opposite to and of greater magnitude than that introduced by said previously named means.

JOHN L. HARRIS. 

